This invention relates to a novel method for removing a phosphor layer from a support surface so that the support may be salvaged and reused. The novel method is particularly useful in preparing a luminescent viewing screen comprising a light-absorbing matrix wherein a defective in-process phosphor layer can be removed without disturbing the underlying matrix.
Some prior color-television picture tubes include a light-absorbing matrix as a structural part of the luminescent viewing screen. In such tubes, a light-absorbing matrix is supported on the inner surface of the faceplate panel of the tube. The matrix has a multiplicity of openings therein, which may be in the shpe of dots or lines, with phosphor filling each opening in the matrix, and with a specular metal layer over the phosphor.
In one sequence of fabrication steps commonly used in the picture-tube industry, the matrix is prepared by reverse printing, as described, for example, in U.S. Pat. Nos. 3,558,310 to E. E. Mayaud and 4,049,452 to E. M. Nekut. After such a matrix is deposited on the inner surface of a panel, a patterned layer of phosphor particles and a binder therefor is deposited photographically in the openings of the matrix. The phosphor layer is dried and then coated with a film of organic polymeric material as described, for example, in U.S. Pat. Nos. 3,582,389 and 3,582,390, both to T. A. Saulnier. The film is then metallized, usually by vapor-depositing aluminum metal thereon followed by baking in air to remove organic matter from the structure.
During the fabrication steps following the deposition of the matrix, some screens are found to be defective; for example, because the phosphor layer is blemished or out of position with respect to the matrix. By a prior salvaging method, the entire screen structure, including the matrix, is stripped from the panel of the tube, and a new screen structure is produced on the salvaged panel. Where the matrix is not defective, considerable savings can be realized if the matrix can be salvaged with the panel.
Attempts have been made to remove the material overlying the matrix by contacting the phosphor layer and film with one of the oxidizing solutions used to develop a matrix. Examples of such oxidizing solutions are disclosed in the Mayaud and Nekut patents cited above. Although most of the overlying material is removed with prior oxidizing solutions, nevertheless enough material remains to consider the panel and matrix unacceptable for recycling.
In other attempts to remove the material overlying the matrix, described in U.S. Pat. No. 4,165,396 issued Aug. 21, 1979 to J. A. Calamari, Jr., before the phosphor layer and film are baked, they are contacted with an alkaline solution, preferably of ammonium hydroxide, until the film is at least partially solubilized. Then the material overlying the matrix and support is flushed with an aqueous medium. It has been found in practice that substantially all of the overlying material is flushed away only if a relatively high-pressure spray or lance is used. A high-pressure spray or lance tends to erode the matrix, sufficiently altering the sizes of the apertures therein so that a substantial proportion of the salvaged matrices must be rejected as out of specification.
The novel method permits the material overlying the matrix to be substantially entirely removed without substantially disturbing or altering the matrix. If no matrix is present, the method may be used as a convenient and safe method for removing a phosphor layer of film from a support surface.